I decided to upgrade to a larger cylinder after a hard seizure on my 2011 Tomos LX. I installed a new 70cc Airsal kit. Without a spark plug in, when I backpedal to turn the engine, it turns smoothly and pushes air out of the spark plug hole. However, when I screw a spark plug in, I cannot backpedal at all to start it and I don't understand why not. The flywheel only turns 3/4 of a turn from one very hard stop to another and the piston moves with it.

Here are some important factors to consider:

- The hard seizure that locked up the old top end was due to a busted needle bearing cage. One of the needles subsequently fused itself into my piston skirt. I can account for all but one or two needles. I couldn't detect any debris in the crank case and the small end of the con rod still looked super smooth. Of course I replaced the needle bearing as well as the wrist pin. Still, maybe there is debris in there somewhere or some other damage caused by the seizure could be causing this problem.

- As I mentioned, I am a total noob. It's possible I just did something wrong when installing the kit. It feels like something is out of place and simply blocking movement

-I was also kind of slow to diagnose the hard seizure, it's possible that I put too much pressure on the pedals attempting to kickstart it free after the seizure. Maybe I've damaged something in the kickstart assembly.